Interference canceling method and apparatus of a multi-mode subtraction type in asynchronous multipath channels of code division multiple access system

Abstract

The present invention provides an interference canceling method and the apparatus of a multi-mode subtraction type in asynchronous multipath channels of CDMA system, which cancel the interference based on the received signal power of each user (or path), which make the selected fingers keep participating in the subsequent cancellation processing with new (more cleaned) input signal, which do a scale factor's processing and a clipper's processing to make the tentative bit decision, which can select the proper interference canceling method among various interference canceling method according to the total number of users in service, the hardware speed to implement the present method and the power spread of received signals, which repeat the selected interference canceling process recursively with a stage of hardware, which can reduce the number of stage compared with parallel interference cancellation method of the prior art in case that the interference canceling apparatus is made up multi-stages, which do overlappingly a canceling process of the last bit of the multiple bits for efficient operation in the asynchronous channel, which reduce the interference according to the power sequence of each multipath signal instead of the power sequence of each user signal made up multipath signals for efficient operation in multipath channels with unequal powers, which can increase the performance and capacity of the CDMA system by reducing the interference produced by a multiple access process in CDMA system with the asynchronous multipath channels.

What is claimed:  
     
       1. An interference canceling method of a multi-mode subtraction type in an asynchronous multipath channels of code division multiple access (CDMA) system, including the steps of: 
       storing a received intermediate frequency (IF) signal, which passed through a root pulse shaping filter and transformed into a baseband signals, to a buffer;  
       inputting the signal outputted in the buffer to each finger of each detector;  
       processing a pseudo-random noise (PN) code acquisition and tracking process in a timing circuit by using the inputted baseband signal;  
       generating a PN code equivalent with a PN code used in the transmitted signal in a PN code generator by using timing information outputted in the timing circuit;  
       demodulating the baseband signal in a demodulator by using the generated PN code and a walsh code;  
       estimating an amplitude and a phase and a power value of channel parameters in channel and power estimator;  
       deciding a ranking of the power values, and selecting a proper IC mode among various IC modes according to a total number of users in service, a hardware speed and a power spread of received signals, and closing a switch  1  (SW 1 ) within each finger of each detector according to a selected IC mode, in a mode selector and a switch controller;  
       combining a signal outputted in L fingers in a maximal ratio combining method, for combining without omitting the power of L multipath signals of each user in a maximal ratio combiner;  
       multiplying a scale value to the combined signal for making a tentative bit decision most approximately to a bit passed through asynchronous multipath fading channels in a scale factor, and doing processing in a clipper;  
       respreading an output signal of the clipper by using a generated PN code and walsh code in a pilot and data spreader of the finger having the closed switch  1  (SW 1 ), and regenerating the baseband signal by multiplying the estimated channel parameters to the output signal of the pilot and data spreader in a estimated channel processor, transforming the regenerated baseband signal into a pulse shaped baseband signal in a pulse shaping filter;  
       adding the pulse shaped baseband signals in an adder;  
       subtracting the added signal from the baseband signal stored in a buffer, and generating an interference-subtracted resultant signal in a subtractor;  
       adding the pulse shaped baseband signals of the finger having the closed switch  1  (SW 1 ) to the interference-subtracted resultant through a feedback path, and generating a clean input signal in an adder;  
       carrying on recursively the interference canceling process on a basis of the clean input signal with a single stage; and  
       deciding the transmitted bit information in a channel decoder and a bit decider by using a signal obtained by a completion of the interference canceling method.  
     
     
       2. The interference canceling method of the multi-mode subtraction type in asynchronous multipath channels of CDMA system as set forth in  claim 1 , wherein said bit decision and cancellation in said asynchronous channel is processed by processing overlappingly a last bit of said multiple bits. 
     
     
       3. The interference canceling method of a multi-mode subtraction type in asynchronous multipath channels of CDMA system as set forth in  claim 1 , wherein said interference cancellation in said multipath channels is processed according to a power sequence of each multipath signal of each user. 
     
     
       4. The interference canceling method of a multi-mode subtraction type in asynchronous multipath channels of CDMA system as set forth in  claim 1 , wherein said maximal ratio combiner combines the signal outputted in L fingers in said maximal ratio combining method, to combine without omitting the power of L multipath signals of each user. 
     
     
       5. the interference canceling method of the multi-mode subtraction type in asynchronous multipath channels of CDMA system as set forth in  claim 1 , wherein said scale factor multiplies the scale value to said combined signal and said clipper processing to make a tentative bit decision most approximately to the bit passed through said asynchronous multipath fading channels. 
     
     
       6. The interference canceling method of the multi-mode subtraction type in asynchronous multipath channels of CDMA system as set forth in  claim 1 , wherein said mode selector and switch controller select a proper interference canceling method among Enhanced Serial Interference Cancellation (ESIC) method and Groupwise ESIC (GESIC) method and Recursive Parallel Interference Cancellation (RPIC) method and GESIC-to-RPIC (GESRPIC) method according to a total number of users in service, the hardware speed and the power spread of received signals. 
     
     
       7. The interference canceling method of a multi-mode subtraction type in asynchronous multipath channels of CDMA system as set forth in  claim 1 , wherein by operation of said mode selector and switch controller, the finger(s) selected at the previous cancellations as well as the finger(s) having the closed switch  1  (SW 1 ) at the current cancellation only participate in the cancellation, and as the number of cancellations increases, the number of fingers having been selected up to the current cancellation increases. 
     
     
       8. The interference canceling method of the multi-mode subtraction type in asynchronous multipath channels of CDMA system as set forth in  claim 1 , wherein an interference canceller of a multi-mode subtraction type processes recursively the interference canceling with a single stage only and reduces a number of adders and connections for subtraction approximately to 1/K of that required for a PIC method. 
     
     
       9. The interference canceling method of a multi-mode subtraction type in asynchronous multipath channels of CDMA system as set forth in  claim 1 , wherein said interference canceller of the multi-mode subtraction type can be implemented with a variable number of stages, and said interference canceller of the multi-mode subtraction type reduces the number of stages compared with the PIC method in case that the interference canceling apparatus is made up multi-stages since said interference canceller of the multi-mode subtraction type works the proper IC operations recursively with a single stage. 
     
     
       10. An interference canceling apparatus of a multi-mode subtraction type in asynchronous multipath channels of code division multiple access (CDMA) system, comprising: 
       a root pulse shaping filter that transforms a received intermediate frequency signal into a baseband signal;  
       a buffer for storing the baseband signal transformed through the root pulse shaping filter;  
       a timing circuit of each finger that processes a PN code acquisition and tracking process with the baseband signal outputted in the buffer as a input signal;  
       a PN code generator that generates a PN code equivalent with a PN code used in the transmitted signal by using timing information outputted in the timing circuit;  
       a demodulator that demodulates the baseband signal by using the generated PN code and a walsh code;  
       a channel and power estimator that estimates an amplitude and a phase and a power value of channel parameters;  
       a mode selector and switch controller that decides a ranking of the power values, and selects a proper interference canceling mode among a various interference canceling modes according to a number of users and a channel environment and hardware speed, and closes a switch  1  (SW 1 ) within each finger of each detector according to a selected interference canceling mode;  
       a maximal ratio combiner that combines a signal outputted in L fingers in a maximal ratio combining method, for combining without omitting a power of L multipath signals of each user;  
       a scale factor that multiplies a scale value to a combined signal for making a tentative bit decision most approximately to a bit passed through the asynchronous multipath channels;  
       a clipper for clipper processing;  
       a pilot and data spreader that respreads an output signal of the clipper by using the generated PN code and walsh code at the finger having the closed switch  1  (SW 1 );  
       an estimated channel processor that regenerates the baseband signal by multiplying the estimated channel parameters to the output signal of the pilot and data spreader;  
       a pulse shaping filter that transforms the regenerated baseband signal into a pulse shaped baseband signal;  
       an adder that adds the pulse shaped baseband signal;  
       a subtractor that subtracts the added signal from the baseband signal stored in the buffer and generates an interference-subtracted resultant signal;  
       an adder of each finger that adds the pulse shaped baseband signal of the finger having the closed switch  1  (SW 1 ) to an interference-subtracted resultant through a feedback path, and generates a clean input signal;  
       an interference canceler that carries on recursively an interference canceling process on a basis of the clean input signal with a single stage; and  
       a channel decoder and a bit decider that decides the transmitted bit information by using the signal which is obtained by a completion of interference canceling process.